OBJECTIVES: I. Determine the therapeutic efficacy and toxicity of cisplatin, gemcitabine, and trastuzumab (Herceptin) in patients with untreated p185-HER2 overexpressing stage IIIB or IV non-small cell lung cancer. II. Determine the pharmacokinetic interactions among these drugs in these patients. III. Assess the pharmacodynamics of these drugs in these patients.